On the other hand, no reason for clients to pay tax on something that is excluded from income. 

The amounts are low enough that, by itself, the MCTR won't generate a CP-2000.  But if there are other omissions on the return, it may or may not be included in the computation.  I am hoping a lot of California practitioners insist on filing returns paying tax on this today, because that makes it more likely that there will be an announcement from IRS tomorrow.